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Abstract

Nanotechnology has brought about revolutionary innovations in many aspects of the oil and gas industry. Nanotechnology generates nanomaterials, which are natural or synthetic materials with at least one dimension at the nanoscale (1–100 nm). Among them, nanoparticles (NPs), in particular, have large surface areas and high volume concentrations. Given these dimensional effects, nanomaterials acquire unique mechanical, chemical, thermal, and magnetic properties and, therefore, have a superior performance than conventional micro and macro materials in a range of oil and gas field applications. Nanomaterials can also be custom functionalized by chemical modifications to meet specific technical requirements. In this review, the developments in the recent years concerning the research on nanotechnology in drilling, completion, reservoir protection, enhance-oil-recovery (EOR), sensing and imaging techniques, stimulation techniques in oil and gas migration and accumulation have been summarized. The aim of this paper was to provide a comprehensive overview of the scientific progress of nanotechnology in the oil and gas research areas, identifying the existing barriers and challenges, and evaluating the technical and economic prospects in this field.

1 Introduction

The oil and gas industry will confront greater technical challenges in the coming decades [1]. With readily exploitable resources diminishing quickly, the difficulty in discovering oil and gas reservoirs is rapidly increasing. In the long run, exploration expenses will continue to increase. Meanwhile, global energy consumption is constantly increasing every year. The industry needs technological innovations to meet this immediate demand. Only a small amount of success has been achieved in solving these problems by use of conventional macro and micro materials [2], [3]. Nanotechnology is an area subject that has had a revolutionary impact on many aspects from medical treatments to electronics [4], [5], [6]. As with these fields, the oil and gas industry is expected to experience such progress [7]. In this case, much attention has been drawn to the innovation and application of nanotechnology in the energy industry. Here we examine the use of nanotechnology to explore the possibilities of improving the functional ability and environmental suitability of materials in the oil and gas industry. Currently, nanotechnology is considered a game changer in exploiting oil and gas resources and is expected to significantly contribute to the development of fossil-based energy technologies over the next 30 years [8]. Much research has reported the development of nanomaterial and nanotechnology and their application in the operation, drilling, and production of oil and gas [9], [10], [11], [12], [13], [14], [15].

The applications of nanomaterials, nanomaterial-based methods, and devices characterized by microstructures are collectively called nanotechnology [8]. Nanomaterials did not only come into existence in recent years, the use of many naturally occurring nanoscale particles dates back to ancient Roman times. What is new to us is engineered nanomaterials with unique chemical effects such as reactivity, physical properties, and electrical conductivity [16]. The design and modification of materials has stimulated an enormous potential for carbon nanotechnology from the outset [17]. This breakthrough has triggered the nanotechnology revolution. It goes to show that the key to the success of nanomaterials has been the modification in nanoscale so that the existing materials acquire novel properties and functionalities making them applicable for certain requirements [5]. Examples of different types of engineered nanomaterials include carbon black, nano-clay, carbon nanotubes, polymeric, metal nanoparticles (NPs), and quantum dots [18].

The particles with a diameter smaller than 100 nm are called NPs. At this size range, surface effects and quantum effects are the two primary factors that make nanomaterials different from macro and micro materials [19]. NPs are excellent tools when used as contrast agents and sensors in different formations. Nanosensors help to illuminate detailed information about the characterization of formation, fluid flow, and fluid type of materials [9]. Metallic coatings made of nanoscale silica, zinc, and zinc-nickel show superior performance in corrosion protection in the oil and gas industry [20], [21].

This article reviews the recent progress of nanotechnology in the oil and gas field and presents potential opportunities and existing challenges of nanotechnology applications in this industry.

2 Nanoparticles (NPs) and nanofluids

The particulate materials with a diameter smaller than 100 nm are called NPs. NPs used in the oil and gas field are generally monodispersed and chemically modified. It has been shown that these NPs consist of the original particles and coating film, which are grafted or covalently linked surface molecules. This enables NPs to have some special physical and chemical properties such as magnetic, electrical and size-dependent properties and affinity, and activity properties. According to different conditions and requirements, using materials with specific particles and coating films significantly improves the engineering efficiency. Through this method, NPs can take advantage of performance gains including (a) light adsorption and emission, (b) adsorption properties, (c) high mechanical strength, (d) superparamagnetism, (e) catalytic properties, (f) high electrical conductivity, and (g) high thermal conductivity [19], [22].

The development in nanotechnology has generated a new type of fluid called “nanofluid”. Nanofluid is defined as a class of fluid that is a base fluid with NPs suspended with it. Its applications include engine cooling, solar water heating, biomedical applications, etc. [23]. Several years ago nanofluids were introduced to the oil and gas industry. Due to progress in this area, nanofluids are now widely used in drilling, completion, enhance-oil-recovery (EOR), and many other applications [24].

3 Stimulations in porous media

The reservoir is a non-homogeneous porous media composed of different minerals. It can be seen as a collection of complex natural nanomaterials, which are usually comprised of nanoscale mineral particles, porosity, and an organic matter cluster. Investigations about the transportation of oil, gas, and NPs in porous media help to increase a further understanding about the oil and gas migration laws and provide an accurate interpretation of hydrocarbon zones [25].

3.1 Oil and gas transport in nanopores

A number of nanotechnology-related simulations have been conducted for oil and gas recovery, especially for those stored in the nanopores of organic-rich shales. Oil and gas show different phase behavior in nanopores. Wang found that the phase transition of resources in nanopores is significantly affected by the distribution of the pore size. Phase transition is a continuous process including the the selection of the most favorable positions, phase change, thermodynamic equilibration, and the selection of the next favorable positions. When the diameter of the pore is larger than 10 nm, the capillary pressure shows insignificant influence on the pressure-saturation relation of the porous media [26]. For hydrocarbon mixtures (of crude oil and natural gas, etc.), flow in the pores with smaller diameters, the interaction between gas and liquid becomes an amplified factor. This interaction tends to show nanopore-confinement effects. The confinement effects such as layering structure and liquid saturation determine the interfacial surface tension (IFT) behavior. When the gas-liquid interface is at an appropriate relative position to the pore wall, IFT significantly decreases compared to gas and liquid in the bulk phase. These results help to discover the mechanism of the phase change in the nanopore media. An investigation revealed that when gas passes through a nanoporous media, the mode can be basically divided into two types: the bulk-gas transfer and adsorption-gas surface diffusion. If the diameter of the pores is less than 4 nm, the surface-diffusion coefficient determines the gas transfer in all the pressure conditions, whereas the slip flow determines gas transfer on the condition that the diameter of the pore is larger than 4 nm. For macropores with a radius that are generally larger than 50 nm, Knudsen diffusion remains the most important factor [27], [28], [29].

3.2 NP transport in porous media

The transport properties of NPs in porous media have been widely studied. Metin et al. studied the rheology property of NP flow in porous media. They pointed out that the viscosity of NP dispersions was largely determined by the particle concentration used in the formation. Besides, the pore morphology and the interaction between the NPs and formation fracture also work in this process. More importantly, it was revealed that the adsorption effect has a large influence on the concentration of the NPs [30]. Abdelfatah et al. then investigated the adsorption and release of NPs. It was observed that there was a negative correlation between the pH, temperature, and rate of NP adsorption. The relative high ionic strength and small NP diameter contributed to the adsorption of the NPs [31]. Zhang found that both reversible and irreversible adsorption of NPs occurred when NPs were transported through water saturated sand packs. Finite capacities exist for both reversible and irreversible absorption. The sites and capacities for reversible adsorption are independent of the irreversible adsorption for many types of NPs. Greater injection concentration, less clay, and smaller flow rate contribute to the increase in the adsorption effect [32].

An experiment conducted by El-Amin and Brahimi showed that when a magnetic field was added onto the magnetic NPs in a porous media, the water saturation, NP concentration, and NP distribution could be affected [33]. Researchers found that the NP-water suspension moved rapidly through the fractures, which enabled the use of NPs to enhance oil recovery of the fractured formation [34]. Recent studies have also revealed that NPs and polymer work well together, which provides the basis of the application in completion and reservoir protection [35].

4 Sensing and imaging

Medical science has developed the technology of using surface-coated NPs as image-enhancing agents for further diagnostics [36]. In a similar manner, the modified NPs can be injected into a reservoir with a fluid, these NPs change the electric, magnetic and acoustic characteristics of formation. The method makes it possible to obtain more information about the porosity, permeability, and temperature of the reservoir.

4.1 Electromagnetic sensing

Magnetic NPs were used as contrast agents for monitoring and surveillance of the reservoir to get accurate reservoir parameters. The fundamental principle is that the magnetic media generate a magnetic field. The magnetic field will slow down the speed of electromagnetic (EM) waves. Then, the distance can be acquired by calculating the transport time difference. After the magnetic NPs pass through the rock fracture, the position of the magnetic NPs can be identified by analyzing the travel time of the EM waves recorded in the transmitter and the receiver. In this method, it is feasible to make a crosswell imaging to find the position of the fluid front. Additionally, these NPs do not need to recover [12], [37]. Ranmani carried out an experiment on ferrofluid, which has stable dispersions of superparamagnetic iron oxide nanoparticles (SPIONs) based on EM conductivity-monitoring technology, to investigate the magnetic tracing of its slug and comparing injected and resident fluids to find the magnetic difference. It was observed that ferrofluid changes the magnetic permeability of certain regions, thereby, enhancing the images of the flood [38]. In another study, researchers used SPION as contrast agents to characterize their impact on nuclear magnetic resonance (NMR) measurements including experiment and simulations. The combination of SPION and NMR relaxometry is capable of improving the characterization of the pore-size distribution and interconnected porosity and fracture work in rocks [39].

4.2 Temperature sensing

Reservoir temperature is one of the crucial parameters in oil and nature gas engineering and geothermal research. Detailed temperature data could provide useful references for inferring reservoir and fracture properties and making decisions about reservoir exploration. However, they are sometimes difficult to directly measure. Conventional reservoir-characterization materials can only acquire the temperature and pressure of the wellbore in that the physical size can restrict their ability for further surveillance. The temperature-sensitive nanosensors (TSNs) are capable of conducting in situ measurements within formations. Nanosensors made of spherically shaped silica NPs significantly decrease the blockage when flowing through the channels of a fracture. Therefore, it is possible for TSNs to transport to areas in the reservoir that other materials cannot access. TSNs show a very high recovery rate. These NPs were also demonstrated to have an ability to estimate the fraction’s aperture [40], [41].

4.3 Optical imaging

Although it has been revealed that oil and gas exist in nanopores of subterranean reservoirs, the detailed process of oil and gas flowing in the rocks with the permeability of the nano-Darcy range remains unclear. Wu et al. proposed a method to obtain a visual representation of the fluid flow behavior in nanoscale channels of formations. They used nanofluidic techniques to establish a pressure-driven flow in the channels, and the used epi-fluorescence microscopy to trace its concentration-dependent fluorescence signal (Figure 1). Therefore, a direct visualization of fluid flow in nanochannels was obtained. It provides a novel idea for analyzing the mechanism of oil and gas flow in certain reservoirs. Current limitations involve the sensitivity and the complex optic arrangement. This method is still at the experimental stage [42], [43].

5 Drilling

Nanotechnology-based drilling products have demonstrated their unique characteristics such as huge surface area, high thermal conductivity, and pollution resistance. Nanomaterials are expected to show excellent fluid properties with very low concentration in fluid systems. They are regarded as the most promising materials to form high-quality mud cake, improve the wellbore stability, and meet complicated requirements during drilling. Hence, this approach is recommended in the application of current and future high-temperature high-pressure (HTHP) drilling operations, unconventional drilling conditions, and deep-water drilling operations [24], [44].

5.1 Nano-enhanced drilling fluid

Fluid loss is the major problem in drilling operations. NPs show various properties depending on the formation types. It is reported that NPs have been used successfully to improve the rheology property and reduce fluid loss [15], [45].

Shakib evaluated several metal NPs, metallic oxide NPs, and nano-clay at low temperatures and low pressure. The properties of these materials were tested in a water-based drilling fluid (WBDF). It was found that all these materials have superior properties over conventional additives. Among them, nano-clay showed superiority to improve rheology properties and reduce fluid loss [46], [47].

Novel water-soluble NPs and polymer systems were proposed to improve the drilling fluid performance. The polymer was used to enhance the rheology properties and dispersion. The NPs were used to make better mud cake to reduce filtration [48].

In the exploration of gas hydrate-bearing sediment, the mining area is in deep water. In these conditions, the temperature is low (under 10°C), and the water pressure is high. The gas hydrate easily decomposes and passes into the wellbore. Then, this free gas will recrystallize with drilling fluid, which results in the blockage of the pipe and an increase in operational risks. Liu revealed that the polymer and SiO2 NPs enhanced the drilling fluids and significantly inhibited the recrystallization effect of free gas. This nano drilling fluid shows good ability in low-temperature conditions. Moreover, in this method, the total cost will be reduced by 15–20%. This approach has great prospects [49].

Recently, Hall et al. synthesized a new kind of cellulose nanofibers (CNFs) as a renewable, non-toxic, and potentially less expensive alternative to synthetic polymers, and a more robust alternative to conventional biopolymers. CNFs show superior performance for rheology and filtration control, which exceeds the thermal stability of xanthan gum. It revealed that the filtration of cationic cellulose nanofibers (Cat-CNF) is far below that of the xanthan gum [50]. Ponmani investigated the thermal and electrical properties of WBDFs. The NPs were CuO and ZnO, and the base fluids were xanthan gum, PEG, and PVP. It revealed that the thermal and electrical properties of the drilling fluid are enhanced by adding NPs. Hence, the nano-enhanced drilling fluid plays an important role in avoiding circulation loss by sealing the formation with both NPs and conventional bulk particles in the fluid system. This method expanded the application of water-based drilling fluid especially in unconventional drilling [51].

5.2 Additives for HTHP drilling fluids

Fe2O3 and Fe3O4 NPs were found to be excellent additives for HTHP drilling fluids. An experiment revealed the fine diffusion properties among the bentonite-based fluid and the superior filtration characteristics of Fe3O4 and Fe2O3 NPs. At an optimum concentration, these NPs bring significant benefits to reduce fluid loss compared to conventional drilling fluids. The property can be improved further after thermal aging at 177°C. The new formulation mainly improves the filter cake properties and reduces fluid loss in static and dynamic conditions. Moreover,Fe3O4 NPs also significantly decease the spurt losses [52], [53]. These NP rheology modifiers show superior performance in high-temperature conditions as well. Only a very low concentration of Fe2O3 NPs can significantly increase the plastic viscosity (PV) of bentonite-based drilling fluid at room temperature. The rheological properties of Fe2O3 NP-based fluids are associated with the electrical resistivity. This correlation provides a new way to predict and control the rheology properties of the drilling fluid in the field [54].

5.3 Improvement of wellbore stability

Maintaining the wellbore stability is always an important part in drilling operations. Recent research has shown that nanomaterials offer new methods to address borehole problems in shales.

5.3.1 Temperature control

The thermal effect is one of the major factors that predominantly affect the shale stability. Conventional methods result in a sharp temperature contrast between drilling fluid and the reservoir, thereby, increasing the chance of borehole instability. Thermoelectric nanomaterials combined with Ni-Fe nanomaterial additives provide a solution for this problem. Thermoelectric nanomaterials could efficiently convert heat energy and cool down the drilling fluid. The Ni-Fe nanomaterials have self-heating properties so that they are able to increase the temperature of the fluid. By adjusting the concentration of these two materials, it is possible to reduce the temperature contrast between the shale and drilling fluid to an optimum value. This approach could miniaturize the thermal factors that influence shale stability [55], [56].

5.3.2 Shale-plugging agent

The primary wellbore instability problems in shale are due to the interaction between the drilling fluid and the reservoir. The fluid shows a negative impact on the stability of the wellbore through entering into formation pores. Conventional macro and micro particles are not small enough to seal the nanopores in the shale formation [57], [58]. The addition of nanomaterials with a very low concentration in the drilling fluid significantly increases the dispersion property [24]. Moreover, nano-based drilling fluid additives successfully improved the wellbore stability using a nontoxic substance [57]. A study revealed that a combination of KCI and Al2O3 NPs could minimize pore pressure by 50% compared with pure NP suspension in deep-water drilling. In this method, Al2O3 particles decrease the pressure by using both chemical potential and plugging effects. The new plugging method leads to a decrease in pore pressure transmission and reduces hydration and swelling in shale formations by delaying the equilibrium state. Additionally, this approach is also a valuable reference to improve the wellbore stability in deep-water drilling [59].

Because of the very high surface area compared to bulk materials, NPs often generate unsaturated chemical bonds, resulting in the surface of the NPs losing electrical neutrality. This mechanism makes nanomaterials acquire adsorption to shales. Hence, nanomaterials show significantly enhanced interaction potentials with the reactive shale [60]. Recently, researchers started to use the absorption of the nanomaterials to improve the shale stability. An investigation indicated that chemically modified graphene had great adsorption in shale. This material can form a thin-film structure on the rock surface. Such a film works efficiently to inhibit the drilling fluid from entering the permeable shale formation. In another study, a kind of nanoterpolymer plugging agent was used, to be absorbed on the rock surface, and then entered the pore throat of the shale by which it significantly reduced the permeability of the shale. In addition, this material shows a resistance to salinity, calcium, and high temperature [61], [62]. In high-angle drilling operations, the highly depleted formation pressures are the most difficult factors to overcome. It has been reported that a nano-sized polymer and modified graphite were used to convert conventional oil-based mud to a customized fluid system. It enabled less borehole stability and enhanced wellbore cleaning in high-angle sections [63].

5.4 Nano-enhanced fracture technology

5.4.1 High-temperature fracturing fluid

Nanomaterials have been used to address certain technological problems in fracturing operations. The HTHP conditions are the primary obstacles of conducting fracturing operation in tight formations. In general, the bottom-hole temperature ranges from 350°F to 400°F. Conventional cross-linked polysaccharide hydraulic-fracturing fluid will form divalent ion scales and damage the formation, which confines its applications [64]. NPs enable a more effective crosslinking process. The nanocrosslinkers reduce the polymer loading and polymer residue of hydraulic fracturing fluids. With this approach, the rheology properties and thermal stability of fracturing fluids are both significantly improved. In addition, some of the experimental results illustrate that part of these gels show no pressure dependency at high temperatures [65], [66].

Recently, nanomaterials have been used as the enhancing additives for viscoelastic surfactant (VES)-based fracturing fluids. With the low molecular weight and a self-assembled micellar structure, the VES fluid can form three-dimensional networks, which contribute to the reduction in surface tension in the fracturing fluid. It has been observed that the addition of NPs improved the thermal stability and decreased the high leak off rates of the VES fluid. The property can be further enhanced by adding a polymer. Though this method has been proven to be highly effective, there are two main shortcomings: a) the rheology properties decrease as the temperature increases; b) the total cost is high at present. This method needs further study [67], [68].

5.4.2 Nano-proppants in tight formations

Nano-proppants were found to have exceptional properties to be proppants. It shows high mechanical strength and reduces elastic modulus. The size of the nano-proppants range from 100 nm to 1 μm. Nano-proppants are capable of penetrating into the existing or generated micro-fractures in tight shale formations. This enables them to prevent fracture closure and provides channels for oil and gas resources [69].

5.4.3 Friction reduction

Nanomaterial is considered as an innovative lubricant additive in the drilling operation. For example, the addition of nickel-based NPs in the drilling fluid significantly reduces the friction drag between the borehole and the drill pipe. Another new kind of micro-nanoparticles (MNPs) mixed with glide graphite was added to enhance the lubricity of the oil-based drilling fluid [70]. It increases the properties of the current equipment and make the system’s performance reach its limit especially in horizontal and extended-reach drilling [71].

Under HTHP conditions, a lubricant with the addition of graphene is crystallized in layers, which makes the tubular surface tend to shear and slide. This method reduces the friction coefficient. Graphene also adds a superior thermal stability to the drilling fluids [72]. It contributes to the improvement of the drilling efficiency and the reduction in the drilling costs.

5.5 Removal of contaminants

With the rising awareness of environmental protection, the oil and gas industry has put more emphasis on reducing adverse impacts on the environment during drilling operations. Nanomaterials are considered as the optimum selection to remove contaminants in that they have superior physical and chemical properties. Magnetic NPs have proved to be excellent adsorbent materials in that they combine unique magnetic properties with good adsorption capacity. It is reported that nano-adsorbents made by amino-functionalized magnetic NPs can be used to remove cadmium ions from drilling fluids. These NPs show a relatively high efficiency at low concentrations compared to conventional treatment materials [73]. Kakade et al. presented a new approach to investigate the feasibility of using magnetic NPs to clean up oil spill in water [74]. A recent study by Li demonstrated an ecofriendly nano adsorbent. This adsorbent is based on lignin-grafted carbon nanotubes. Its molecular structure is tridimensional, which gives it great adsorption properties for lead ions and oil droplets. This method exhibits a good prospect in removing contaminants from the environment [75].

6 Enhance oil recovery

6.1 Stabilizers of emulsion and foam

Foam and emulsion are important materials in EOR operations. A number of investigations have been carried out to find a solution for maintaining the stability of these fluids. NPs have been noticed to have a potential to be good interfacial stabilizers due to their unique surface properties. This research led to a new promising technical area. Foams are dispersion systems formed by the dispersal of insoluble gases in liquids. The foams naturally tend to separate from the liquid, which results in the instability of the mixture. The effect of the NPs to stabilize the foams in this process has been illustrated [13]. Investigations have shown that it is the detachment energy, rather than the high concentration of the NPs, that determine the stability of the foams. The detachment energy is partly determined by the contact angle, which is correlated with the hydrophilicity and hydrophobicity of the NPs [76]. Singh et al. prepared and evaluated surface-modified silica NPs, which were alumina-coated to obtain partial hydrophobization. It was observed that the foam stabilized by the surface-modified NPs is superior to that obtained by the conventional surfactant. This approach enabled the potential to use NPs as a surfactant to stabilize foam in porous media [77]. In related studies, the experimental data showed that the mixture of α olefin sulfonate (AOS) solution with NPs generated stronger foams than the AOS solution alone [76].

Emulsions share similar properties with foams. The particles used as emulsion stabilizers should have good wettability in both liquids. In addition, in order to avoid precipitation and agglomeration, the flocculation effect of these particles should be weak. Many types of materials have been tested according to this criterion [13]. A microfluidic study (Figure 2) was conducted to investigate the extent of the NP effect on emulsion dynamic stability and the mechanism of this effect. The addition of surfactant to NPs showed a synergistic effect to prevent droplet coalescence and improved the stability of the system [78], [79].

Figure 2:

The schematic of the microfluidic design [78].

6.2 Rock wettability alteration

Wettability is the inclination of a liquid to spread over a solid surface. In an oil-recovery study, rock wettability was an important factor that dominated fluid separation and distribution in the pores. Nanomaterials are widely used in wettability alteration for EOR. Among them, silica and poly silicone NPs show superior properties [80], [81]. Roustaei investigated the effect of silica NPs in the wettability modification of a carbonate reservoir through adsorption on the rock surface. It was observed that silica NPs could increase the IFT of oil-water and resulted in the spontaneous imbibition of water into small pores. Compared with the conventional surfactant, the average recovery ratio increased by 10% with the use of silica NPs-based nanofluid (Figure 3) [82]. In water flooding, reducing the particle size of silica NPs and coating them with xanthan gum have been proven to be effective methods to improve the ultimate recovery [83]. A recent investigation was conducted to evaluate the properties of several kinds of polysilicon NPs. It was found that NWP NPs had strong wettability-alteration ability and HLP NPs could significantly reduce oil-water IFT. Both of the two agents improved the EOR performance [84].

Figure 3:

Simplified diagram of the NPs in the interface of oil and water [82].

6.3 Heavy oil recovery

Oil viscosity and relative permeability are the two main factors that control heavy oil mobility. Nanofluids have been found to have an inhibition effect on the asphaltene deposition, which prevents the blockage of oil flow and enables effective oil mobility [85], [86]. An investigation conducted by Zabala et al. revealed that the use of oil-based nanofluids (OBNs) reduced the oil viscosity at static conditions by approximately 98% without continuous injection [87]. Metal and metal oxide NPs have unique properties compared to their macroscopic counterparts. These NPs were used as considerable adsorbents and catalysts for heavy oil recovery [88]. Hamedl-Shokrlu revealed that the nickel NPs catalyzed the aquathermolysis process of steam stimulation. Shokrlu et al. studied the kinetics of nickel NPs in this process. Nickel NPs are capable of reducing the activation energy of the main aquathermolysis reaction. The principle is that the nickel NPs break the C-S bonds in the compounds, which reduce the length of their molecular chain. Through this method, the concentration of the components with the carbon chain length, which is more than 31, is decreased resulting in the reduction in oil viscosity. Therefore, the energy usage is more efficient, and the heavy oil recovery is significantly increased [89], [90].

7 Completion and reservoir protection

7.1 Fine migration and scale formation control

In the whole process of drilling, completion, and downhole operation in oil and gas field exploitation, the phenomenon of permeability decrease in oil and gas reservoirs is collectively called oil and gas reservoir damage. Among the many factors leading to permeability decrease, fine migration and scale formation are the main factors. Recently, nanomaterials have been used to solve this problem. Bedrikovetsky et al. established a mathematical model to describe the injectivity decline. They found that formation damage coefficients are in positive correlation with the particle concentration in the formation [91]. Based on this, Yuan used the maximum retention concentration as a metric to evaluate the inhibition property of nanomaterials in the process of fine migration. According to their study, it is feasible to enhance the capability of porous media to capture fines by coating the porous media with NPs [92]. In this way, researchers use magnesium oxide, silicon dioxide, and aluminum oxide to reduce accumulation of fines in the formation and prevent clays from swelling. The experimental results showed that a low concentration of NPs has good ability in mitigating fine migration [93], [94], [95].

Polymer scale inhibitors have wide applications in the oil and gas industry in that they have good thermal stability and environmental suitability, while their relatively low squeeze efficiency limits their properties and further applications. The combination of NPs and polymer inhibitors expands their use. The mixtures can be delivered into crushed formation materials for scale control. These inhibitors based on polymer nanocomposites include AlO(OH)-sulfonated polycarboxylic acid, Al-sulfonated polycarboxylic acid, Si-Zn-methylenephosphonic acid, and nanoscale metal-phosphonate particles [96], [97], [98], [99].

7.2 Oil cement system

In the oil and gas cement system, it is crucial for a cement sheath to maintain the long-term integrity of the wells. The temperature condition is an important factor of the oil cement system. Excessive low temperatures can result in the extension of delay time and increase the cost of the project. Pang investigated nanosilicas as additives for low-temperature conditions. It was observed that the use of nanosilicas increased cement hydration without a decrease for a long time. To reduce the particle size and increase the aspect ratios, both contribute to the nanosilica performance. Nanosilica also shows superior compatibility with calcium chloride [100]. The HPHT condition is another problem. An experiment conducted by Murtaza et al. concluded that nanoclay enhanced oil cement slurry. The enhanced cement had compressive strength and rheological properties under conditions of the API standard [101].

Bulk shrinkage is a big problem of oil cement applications in wells, which leads to the loss of long-term zonal isolation. Because of the nanostructure and hydration reactivity, MgO NPs show expansive properties for the cement system. An investigation by Jafariesfad et al. showed that MgO NPs significantly improved the expansion of cement and prevented bulk shrinkage. They also found that the addition of MgO NPs significantly reduced the setting time compared with the original system [102].

8 Discussion

We have reviewed much of the current research concerning the application of nanomaterials in the oil and gas industry. The technical and economic prospects of nanomaterial and nanotechnology are significant. Nanopores are common in the stratum, especially, in shale formation. The transport of oil and gas in these nanopores was a major factor to impact the yield of oil and gas. The use of nanotechnology to improve the transport of oil and gas in these nanopores will increase the yield of oil and gas significantly. The sensibility of nanomaterials was stronger than that of micro materials. The nanomaterials can be used as sensors to improve the sensibility of the equipment or be coated on the surface of the equipment. These nanomaterial sensors will improve the accuracy and veracity of the equipment greatly, and then, the work time will be reduced significantly. The addition of nanomaterials to the HPHT drilling fluid system will improve the quality of the filter cake and reduce the volume of fluid loss. The apparent viscosity of the drilling fluid system was kept stable with the nanomaterial to maintain the good rheological properties. What is more important, the use of nanomaterials in water-based drilling fluids for shale formation was easy for keeping the stability of the wellbore. These nanomaterials entered into the nanopores and plugged them. As is well known, the instability of the wellbore for shale information was a worldwide problem. Maybe, the use of the nanomaterials can solve this problem. Nano emulsifiers can enhance the stability of the oil-based drilling fluid system and increase the temperature of the application. Nano meter oil displacement agents with good rheological capability were placed into the stratum easily and improved the displacement efficiency. However, many of them are still at the experimental level. The industrial product is not yet prepared. How to make such a small material has not been solved completely yet. The equipment and preparation technology is limited to the development of the nanomaterials. The aggregation of the nanomaterials in the wellbore fluid is another major factor to limit the application of the nanomaterials. Such a small material is unstable in the wellbore fluid. They tend to aggregate and form the marco material, and it follows that the properties of the nanomaterials were weakened. How to disperse the nanomaterials and keep their stability is the key technology to develop and apply the nanomaterials in the oil and gas industry. The cost of the nanomaterials is high, and how to lower the cost of the nanomaterial is an urgent problem. The interaction mechanism of the nanomaterials is incomplete. Explorations and research of the interaction mechanisms of the nanomaterials need to be studied.

9 Conclusions

According to this review, the following conclusions have been drawn:

Nanomaterials have significantly different properties, i.e. mechanical, chemical, thermal, and magnetic properties compared to their macroscopic counterparts. This enables their ability to solve problems that the conventional methods cannot address.

The large surface-to-volume ratio and huge particle number in one unit mass make nanomaterials significantly improve the fluid properties in the oil and gas industry.

Owing to the nanostructuring and nanoengineering, the tailored nanomaterials become excellent and desirable materials to meet the requirements of oil and gas production.

Although challenges exist for nanomaterials, the application of nanotechnology will raise the working efficiency, promote the technology development, and greatly enhance the overall strength of the oil and gas industry.

Acknowledgments

We would like to thank the China Postdoctoral Fund (H29216), National Natural Science Foundation of China (Funder Id: 10.13039/501100001809, J218076), and the National Key R&D Program of China (2016YFE0202200) for the financial support for this work.

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